Image processor and image processing method

ABSTRACT

Inputted image data is converted to M number of multi-value data having a lower resolution than the inputted image data, and after quantization processing has been performed for each of the M number of multi-value data, an image is printed by M number of relative movements (M-pass printing) that corresponds to the M number of quantized data. By doing so, when compared with the case in which a resolution reduction process is not performed, it is possible to suppress the number of pixels that become the object of quantization processing, and it becomes possible to output an image with no fluctuation in image density or density unevenness without a decrease in the processing speed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image processor and image processingmethod that process multi-value image data that correspond to the samearea in order to print an image in the same area by relatively moving aprinting unit or a plurality of printing element groups a plurality oftimes with respect to the same area of a printing medium.

2. Description of the Related Art

In inkjet printing devices, a multipass printing method that prints byperforming a plurality of printing scans of image data to be printed inthe same area of a printing medium is known as a technique for reducingdensity unevenness and stripes. However, recently, by performingmultipass printing, a new adverse effect of image due to deviation ofprint position among printing scans is viewed with suspicion. Here,deviation of the printing position among printing scans is, for example,deviation between a dot group that is printed in a first printing scanand a dot group that is printed in the second printing scan in the samearea as the first printing scan. Deviation of these dot groups is causedby fluctuation in the distance between the printing medium and ejectionface (paper distance), fluctuation in the conveyed amount of theprinting medium, and the like, when this happens, the dot coverage rateon the paper fluctuates, which causes density fluctuation and densityunevenness of an image. Therefore, recently, a method for processingimage data during multipass printing that is capable of handlingdeviation in the printing position between planes that occurs due tothese kinds of fluctuations in printing conditions is desired.

In Japanese Patent Laid-Open No. 2000-103088, an image data processingmethod is disclosed for suppressing adverse effects to an image asdescribed above. This patent application focuses on the cause offluctuation in image density caused by fluctuation in various printingconditions being that the binary image data that are printed indifferent printing scans are in a complementary relationship with eachother. In addition, in order to solve this problem, this patentapplication discloses a method for dividing image data in themulti-value image data stage before binarization in order to correspondto different printing scans, and then independently (uncorrelated)binarizing the multi-value image data after being divided.

FIG. 8A is a diagram that illustrates the configuration of dots whenimage data is divided and binarized according to the method of JapanesePatent Laid-Open No. 2000-103088. In this figure, the black dots 1501are printed in the first printing scan, the white dots 1502 are printedin the second printing scan, and the gray dots 1503 are printed thefirst printing scan and second printing scan overlap. Here, there is nocomplementary relationship between the dots that are printed in thefirst printing scan and the dots that are printed in the second printingscan. Therefore, there are portions (gray dots) 1503 where two dotsoverlap, and there are also blank areas where no dots are printed.

In this kind of dot arrangement, the dot coverage rate on the printingmedium does not fluctuate much even though the dot group that is printedin the first printing scan and the dot group that is printed in thesecond printing scan shift the amount of one pixel in the main scanningdirection or sub scanning direction. This is because new areas wheredots printed in the first printing scan overlap dots printed in thesecond printing scan appear, however; there are also portions where twodots that were originally supposed to overlap no longer overlap.Therefore, when performing judgment over a somewhat large area, the dotcoverage on the printing medium does not fluctuate much, and thus it isalso difficult for changes to occur in the image density. In otherwords, by employing the method of Japanese Patent Laid-Open No.2000-103088, it is possible to suppress the occurrence of densityfluctuation and density unevenness in an image even when fluctuation inthe distance between the printing medium and ejection face (paperdistance), or fluctuation in the conveying amount of the printing mediumoccurs.

However; when using the method disclosed in Japanese Patent Laid-OpenNo. 2000-103088, the number of pixels that are to be the object ofquantization processing increases by the amount of the divided planes.Therefore, it takes more time to complete quantization when comparedwith the case in which quantization is performed for just one gradationplane, and thus a new problem occurs in that the processing speedbecomes slower. In order to avoid this problem, a large capacity memorycan be prepared, or a CPU can be prepared that has superior processingcapability, however; the cost of the device then increases.

SUMMARY OF THE INVENTION

The object of the present invention is to solve the problems describedabove. In other words, the object of the present invention is to providean image processor and image processing method that are capable ofoutputting images in multipass printing that have no fluctuation inimage density or density unevenness due to deviation during printing,and are capable of outputting such images without a drop in processingspeed or increase in cost.

The first aspect of the present invention is an image processor thatprocesses input image data that corresponds to a pixel area in order toprint dots in the pixel area on a printing medium by M number ofrelative movements between a printing unit that prints dots and theprinting medium, comprising: a unit configured to convert the inputimage data to M number of multi-value data, having lower resolution thanthe input image data, in order to correspond to the M number of relativemovements; a unit configured to quantize each of the M number ofmulti-value data and to create M number of quantized data having a lowernumber of levels than the multi-value data; and a unit configured tobinarize each of the M number of quantized data, and create M number ofbinary data having a higher resolution than the quantized data so thatthe printing unit can print dots in the pixel area by the M number ofrelative movements.

The second aspect of the present invention is an image processor thatprocesses input image data that corresponds to a pixel area in order toprint in the pixel area on a printing medium by M number of relativemovements between a printing unit that prints dots and the printingmedium, comprising: a setting unit configured to set one mode from amonga plurality of printing modes that include a first mode for printing inthe pixel area by performing M number of relative movements, and asecond mode for printing in the pixel area by performing N (N>M) numberof relative movements; a unit configured to convert the input image datato M number of multi-value data, having a resolution that is lower thanthe resolution of the input image data, in order to correspond to the Mnumber of relative movements when the first mode has been set by thesetting unit; a unit configured to quantize each of the M number ofmulti-value data and create M number of first quantized data having anumber of levels that is less than the multi-value data; a unitconfigured to binarize each of the M number of first quantized data, andcreate M number of binary data having a higher resolution than the firstquantized data so that the printing unit can print dots in the pixelarea by the M number of relative movements; a unit configured toquantize the input mage data and create second quantized data when thesecond mode has been set by the setting unit; and a unit configured todivide the second quantized data into N number of divisions and create Nnumber of binary data so that the printing unit can print dots in thepixel area by N number of relative movements.

The third aspect of the present invention is An image processing methodthat processes input image data that corresponds to a pixel area inorder to print dots in that pixel area on a printing medium by M numberof relative movements between a printing unit that prints dots and theprinting medium, comprising the steps of: converting the input imagedata to M number of multi-value data, having lower resolution than theinput image data, in order to correspond to the M number of relativemovements; quantizing each of the M number of multi-value data, andcreating M number of quantized data having a lower number of levels thanthe multi-value data; and binarizing each of the M number of quantizeddata, and creating M number of binary data having a higher resolutionthan the quantized data so that the printing unit can print dots in thepixel area by the M number of relative movements.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram for explaining the steps of image processingof a first embodiment when completing an image in the same area of aprinting medium by 2-pass multipass printing;

FIGS. 2A and 2B are perspective diagrams and illustrate a photo directprinter of an embodiment of the present invention, and the printing unitof a printer engine;

FIG. 3 is a block diagram that illustrates the configuration of PDprinter control according to an embodiment of the present invention;

FIGS. 4A to 4H are diagrams for explaining the dot overlap rate;

FIG. 5 is a diagram that illustrates one example of a mask that can beused in the present invention;

FIG. 6 is a diagram that illustrates the relationship between thedistribution rate and dot overlap rate;

FIGS. 7A and 7B are diagrams that illustrate one example of anerror-diffusion matrix that is used in quantization processing;

FIGS. 8A to 8C are diagrams for explaining the relationship between thedot overlap state or the dot dispersion state and graininess;

FIG. 9 is a flowchart for explaining the processing steps that areexecuted by the quantization processing unit of a third embodiment;

FIG. 10 is a diagram for explaining the dot overlap rate when indexexpansion processing is performed;

FIGS. 11A and 11B are diagrams for explaining the discharge outlet arraystate of a printing head that can be applied to embodiments of theinvention;

FIG. 12 is a schematic diagram for explaining the dot arrangementpattern and data conversion method;

FIG. 13 is a diagram for explaining the correlation between one exampleof results from a quantization process, which is performed usingthreshold values that are entered in a specified threshold value table,and input values (K1 ttl and K2 ttl);

FIG. 14 is a block diagram showing the relationship of FIGS. 14A and14B;

FIG. 14A and FIG. 14B are block diagrams for explaining the steps ofimage processing that is executed in a second embodiment;

FIG. 15 is a block diagram showing the relationship of FIGS. 15A and15B;

FIG. 15A and FIG. 15B are block diagrams for explaining the steps ofimage processing executed in a third embodiment;

FIG. 16 is a diagram that illustrates one example of a dot arrangementpattern that is used in an index expansion process;

FIG. 17 is a diagram that illustrates one example of a dot arrangementpattern that is used in an index expansion process; and

FIG. 18 is a diagram of a detailed example of the image processingillustrated in FIG. 1.

DESCRIPTION OF THE EMBODIMENTS

In the following, embodiments of the present invention will be explainedin detail with reference to the accompanying drawings.

The embodiments explained below use an inkjet printer as an example,however; the present invention is not limited to an inkjet printer. Theinvention can be applied to devices other than an inkjet printer as longas the device can print an image on a printing medium via a printingunit that prints dots while moving relative to the printing medium.

The “relative movement (or relative scanning) between the printing unitand the printing medium is an operation of relatively moving (scanning)the printing unit with respect to the printing medium, or an operationof relatively moving (conveying) the printing medium with respect to theprinting unit. The printing unit is one or more printing element group(nozzle array) or one or more printing head.

In the image processor explained below, data processing is performed inorder to print images in the same area by relatively moving a printingunit a plurality of times, or relatively moving a plurality of printingelement groups with respect to the same area of the printing medium(specified area). Here, the “same area (specified area)” is “one pixelarea” on a micro scale, or on a macro scale, “an area that can beprinted by one relative movement”. That the area “may also be called apixel area (simply a “pixel”)” means that the area is the minimum unitfor which gradation expression is possible using multi-value image data.On the other hand, “an area that can be printed by one relativemovement” is an area on the printing medium that the printing unitpasses over during one relative movement, or is an area smaller thanthat area (for example, one raster area). For example, when executingthe multipass mode as illustrated in FIG. 10, on a macro scale, oneprint area in the figure can also be defined as the same area.

<Summary Explanation of the Printer>

FIG. 2A is a perspective drawing of a photo direct printer (hereafterreferred to as a PD printer) 1000 of an embodiment of the presentinvention, or in other words, an image formation device (imageprocessor). The PD printer 1000 comprises: a normal function ofreceiving and printing data from a host computer (PC), a function ofdirectly reading and printing an image that is stored in a memory mediumsuch as a memory card, and a function of receiving and printing an imagefrom a digital camera, PDA or the like.

In FIG. 2A, 1004 is a discharge tray into which printed paper can bestacked, and 1003 is an access cover that a user can open or close whenreplacing the printing head cartridge or ink tank that are stored in themain unit. Menu items for setting various conditions related to printing(for example, the type of printing medium, image quality, and the like)are displayed on the control panel 1010 that is provided on the uppercase 1002, and a user can set these items according to the type and useof the image to be output.

In the figure, 1007 is an auto supply unit that automatically suppliesprinting medium to the main unit, 1009 is a card slot into which anadapter to which a memory can be mounted is inserted, and 1012 is a USBterminal for connecting a digital camera. A USB connector for connectinga PC is provided on the rear surface of the PD printer 1000.

<Electrical Specifications of the Control Unit>

FIG. 3 is a block diagram that illustrates the construction of the mainparts for control of the PD printer 1000 of embodiments of the presentinvention. In FIG. 3, the same reference numbers are used for parts thatare common with those in drawings described above, and explanations ofthose parts area omitted. As will be made clear in the explanationbelow, the PD printer 1000 functions as an image processor.

In FIG. 3, 3000 is a control unit (control board) and 3001 is an imageprocessing ASIC (special customized LSI). In the figure, 3002 is adigital signal processor (DSP) having an internal CPU, and controls thevarious control processing and various image processing described later.Reference number 3003 is a memory having a program memory 3003 a thatstores the control programs for the CPU of the DSP 3002, a RAM area thatstores programs during execution, and a memory area that functions as awork memory and stores image data. Reference number 3004 is a printerengine, and here a printer engine is mounted for an inkjet printer thatprints color images using a plurality of colors of ink. In the figure,3005 is a USB connector used as a port for connecting a digital camera(DSC) 3012. Reference number 3006 is a connector for connecting a viewer1011. Number 3008 is a USB hub, and when the PD printer 1000 printsbased on image data from a PC 3010, lets the data pass as is from the PC3010 to the printer engine 3004 via the USB 3021. In doing so, theconnected PC 3010 can execute printing by exchanging data and signalsdirectly with the printer engine 3004 (functions as a typical PCprinter).

Reference number 3009 is a power-supply connector, and DC voltage thatis converted from the commercially available AC is input from the powersupply 3019. The PC 3010 is a typical personal computer, 3011 is amemory card (PC card) as mentioned above, and 3012 is a digital camera(DSC). The exchange of signals between this control unit 3000 and theprinter engine 3004 is performed via the USB 3021 described above, or anIEEE-1284 bus 3022.

<Summary of the Printing Unit>

FIG. 2B is a perspective drawing that illustrates the printing unit ofthe printer engine unit of a serial-type inkjet printer of theembodiments of the present invention. The auto feed unit 1007 feedsprinting medium P to the nip section of a conveying roller 5001 andpinch roller 5002 that follows it, which are located on the conveyingpath. After that, the printing medium P is conveyed by the rotation ofthe conveying roller 5001 in the direction of arrow A in the figure (subscanning direction) while being supported and guided over the platen5003. The pinch roller 5002 is elastically pressed against the conveyingroller 5001 by a pressure unit such as a spring (not shown in thefigure). The conveying roller 5001 and pinch roller 5002 are componentsof a first conveying unit on the up-line side in the conveying directionof the printing medium.

The platen 5003 is located at the printing position that faces a surface(ejection face) on which the discharge outlets of the inkjet typeprinting head 5004, and by supporting the rear surface of the printingmedium P, the distance between the rear surface of the printing medium Pand the ejection face is kept at a constant distance. The printingmedium P that is conveyed over the platen 5003 and on which printing isperformed is held between a rotating discharge roller 5005 and spurs5006, which are rotating bodies that follow the discharge roller 5005,conveyed in the A direction and discharged to the paper discharge tray1009 from the platen 5003. The discharge roller 5005 and spurs 5006 arecomponents of a second conveying unit that is located down-line in theconveying direction of the printing medium.

The printing head 5009, with the ejection face facing the platen 5003and printing medium P, is mounted in a carriage 5008 such that it isremovable. The carriage 5008 is driven back and forth by the drivingforce of a carriage motor E0001 along two guide rails 5009 and 5010, andwhile moving, the printing head 5004 executes the ink dischargeoperation according to a print signal. The direction that the carriage5008 moves in is the direction that crosses the direction (direction ofarrow A) in which the printing medium is conveyed, and is called themain scanning direction. On the other hand, the conveying direction ofthe printing medium is called the sub scanning direction. Printing isperformed on the printing medium P by alternately repeating the mainscan by the carriage 5008 and printing head 5004 (movement thataccompanies printing) and conveying of the printing medium (sub scan).

FIG. 11A is diagrams illustrating the case in which the printing head5004 used in the embodiments is observed from the discharge outletformation surface. In the figure, 41 is a Cyan nozzle array (printelement group), 92 is a Magenta nozzle array, 43 is a Yellow nozzlearray and 44 is a Black nozzle array. The width in the sub scanningdirection of each nozzle array is d, and printing having a width d ispossible in one scan.

Each of the nozzle arrays 41 to 44 is such that a plurality of nozzlesthat discharge ink drops is arranged in the sub scanning direction atintervals of 600 dpi (dots/inch), or in other words, approximately 42μm. Each individual nozzle comprises a discharge outlet that is theoutlet when discharging ink, an ink path for directing the ink to thedischarge outlet, and electrothermal conversion element that causes filmboiling to occur in the ink near the discharge outlet. With this kind ofconstruction, by applying a voltage pulse to the individualelectrothermal conversion elements according to a discharge signal, filmboiling occurs in the ink near the electrothermal conversion elements,and an amount of ink corresponding to the growth of generated bubblesbecomes a suitable amount of liquid droplets and is discharged from eachof the discharge outlets.

The printing apparatus of this embodiment is able to execute multipassprinting, so that in the area that can be printed during one printingscan by the printing head 5004, an image is gradually formed byperforming printing scanning a plurality of times. When doing this, byperforming the conveying operation an amount smaller than the width ofthe printing head 5004 between each printing scan, density unevenness orstripes due to variation in each individual nozzle can be reduced.

Embodiment 1

FIG. 1 is a block diagram for explaining the steps of the imageprocessing of an embodiment in which an image is completed in the samearea of a printing medium by using 2-pass multipass printing. In thisembodiment, the control unit 3000 comprises a multi-value image datainput unit (61), color conversion/image data division unit (62),processing resolution setting unit (60), gradation correction processingunits (63-1, 63-2), and quantization processing units (65-1, 65-2).

In this embodiment, the RGB multi-value image data that is input to themulti-value image data input unit 61 from an external device is taken tobe image data in which individual pixel for each color are expressed in8 bits (256 values) and have a resolution of 600 dpi×600 dpi. Inaddition, the color conversion/image data division unit 62 converts thisinput image data (256-value RGB data) to 2 groups of multi-value imagedata (256-value density data) that corresponds to the ink color (CMYK).In this embodiment, construction is such that the resolution of thedensity data from the color conversion/image data division unit 62 isadjusted according to the resolution set by the processing resolutionsetting unit 60. For example, when the processing resolution settingunit 60 designates a resolution of 600 dpi×300 dpi, the colorconversion/image data division unit 62 outputs two groups of 256-valuedensity data corresponding to the ink color (CMYK) at a resolution of600 dpi×300 dpi.

Continuing, in the gradation correction processing units (63-1, 63-2)and quantization processing units (65-1, 65-2), image process isperformed at 600 dpi×300 dpi. Therefore, in each processing unit, thenumber of pixels to be processed is reduced by half compared with whenperforming processing at 600 dpi×600 dpi. However, due to the divisionprocess, the object of processing is doubled to two planes, so as aresult, the number of times that processing is performed is the same asthe conventional method in which the division process was not performed(method of Japanese Patent Laid-Open No. 2000-103088) is not employed),so it is possible to avoid the new problem that was explained in thesection of background of the invention. In FIG. 1, an example is givenin which the processing resolution setting unit 60 designates aresolution of 600 dpi×300 dpi, however; the resolution of themulti-value density data that is output from the color conversion/imagedata division unit 62 can be set case by case.

This kind of resolution conversion process by the color conversion/imagedata division unit 62 is possible by performing an averaging processaccording to the resolution designated by the processing resolutionsetting unit 60. For example, when the designated resolution is 600dpi×300 dpi as in this example, the color conversion/image data divisionunit 62 first calculates the average value of input image data (RGB) oftwo adjacent pixels in the vertical direction (sub scanning direction)among the pixels arranged 600 dpi×600 dpi. Then by referencing a3-dimensional lookup table (LUT) that is prepared in advance, it ispossible to obtain multi-value data (CMYK) for the first printing scan,and multi-value data (CMYK) for the second printing scan.

In a different method, it is possible to reference a 3-dimensional LUTfor a 600 dpi×600 dpi as is, and to first obtain multi-value data (CMYK)for the first printing scan, and multi-value data (CMYK) for the secondprinting scan having a 600 dpi×600 dpi resolution. In this case, bycalculating the average value of two adjacent pixels in the verticaldirection of the 600 dpi×600 dpi CMYK values obtained in that way, it ispossible to obtain the 600 dpi×300 dpi multi-value data for the firstprinting scan and for the second printing scan. In either case, it ispossible to use the same 3-dimensional LUT regardless of the resolutionthat was designated by the processing resolution setting unit 60.

The processing after the gradation correction processing is performedindependently and simultaneously for each color CMYK, so the followingexplanation will be for just one gradation color (for example, black).The 600 dpi×300 dpi multi-value data that was generated by the colorconversion/image data division unit 62 is sent to the respectivegradation correction processing unit 63-1 and 63-2, where gradationcorrection processing is performed using a 1-dimensional LUT. As aresult, 600 dpi×300 dpi multi-value data 64-1 for the first scan isoutput from the gradation correction processing unit 63-1, and 600dpi×300 dpi multi-value data 64-2 for the second scan is output from thegradation correction processing unit 63-2.

The multi-value data 64-1 for the first scan and the multi-value data64-2 for the second scan further undergo quantization processing by thequantization processing units 65-1 and 65-2. In the quantizationprocessing unit 65-1 of this embodiment, the 600 dpi×300 dpi multi-valuedata 64-1 for the first scan that is represented by 8-bit 256 values isconverted to 600 dpi×300 dpi quantized (3-value) data 66-1 for the firstscan that is represented by 2-bit 3 values. In the quantizationprocessing unit 65-2 of this embodiment, the 600 dpi×300 dpi multi-valuedata 64-2 for the second scan that is represented by 8-bit 256 values isconverted to 600 dpi×300 dpi quantized (3-value) data 66-2 for thesecond scan that is represented by 2-bit 3 values. The quantizationmethod that is employed by these two quantization processing units 65-1and 65-2 is a typical multi-value (3-value) error diffusion method.

When doing this, a certain number of locations of overlapping dots thatare printed during two scans occurs, so in two error diffusionprocesses, it is preferred that different diffusion matrices be used.For example, in the quantization processing unit 65-1, the diffusionmatrix illustrated in FIG. 7A can be used, and in the quantizationprocessing unit 66-2, the diffusion matrix illustrated in FIG. 7B can beused.

After 3-value image data 66-1 and 66-2 are obtained from thequantization processing units 65-1 and 65-2, the data are sent to theprinter engine 3004 illustrated in FIG. 3 via an IEEE 1284 bus 3022. Thefollowing processing is executed by the printer engine 3004.

In the printer engine 3004, the 3-value data 66-1 for the first scanundergoes processing by the first scan index expansion processing unit67-1 and is converted to 600 dpi×600 dpi 2-value data 68-1 for the firstscan that is expressed by 1-bit 2 values. In addition, the 3-value data66-2 for the second scan undergoes processing by the second scan dotarrangement pattern processing unit 67-2 and is converted to 600 dpi×600dpi 2-value data 68-2 for the second scan that is expressed by 1-bit 2values.

FIG. 12 is a schematic diagram for explaining the dot arrangementpattern referenced by the index expansion processing unit 67-1 and 67-2and data conversion methods. The left side of the figure illustrates apixel having a 3-value level that is input to the index expansionprocessing unit 67-1 or 67-2, and has one of levels 0 to 2. On the otherhand, the right side of the figure illustrates a dot arrangement patternthat is selected to correspond to the respective level. Each pixelcorresponds to two 600 dpi×600 dpi sub pixels, and one dot can beprinted per one sub pixel.

As illustrated in the figure, when the input level is 0, a dot patternis selected in which no dots are printed in either of the two subpixels. In other words, 600 dpi×300 dpi input data having level 0 isconverted to two 600 dpi×600 dpi output data (level 0 and level 0). Whenthe input level is 1, a dot arrangement pattern is selected in which adot is printed in one of the two sub pixels and no dot is printed in theother. In other words, 600 dpi×300 dpi input data having level 1 isconverted to two 600 dpi×600 dpi output data (level 1 and level 0, orlevel 0 and level 1). Furthermore, when the input level is 2, a dotarrangement pattern is selected in which a dot is printed in both subpixels. In other words, 600 dpi×300 dpi input data having level 2 isconverted to two 600 dpi×600 dpi output data (level 1 and level 1).

Here, focusing in on one 600 dpi×600 dpi pixel (on sub pixel), no blackdots are printed in the sub pixel wherein the binary data 68-1 for thefirst scan and the binary data 68-2 for the second scan are both level0. Moreover, only one black dot is printed in the sub pixel wherein oneof the binary data 68-1 for the first scan and the binary data 68-2 forthe second scan is level 0 and the other is level 1. Furthermore, twoblack dots are overlapped and printed in the sub pixel wherein binarydata 68-1 for the first scan and the binary data 68-2 for the secondscan are both level 1.

After that, the binary data 68-1 for the first scan is stored in thebuffer 69-1 for the first scan, and printed in the first scan by thenozzle array 44 (black nozzle array) in a unit area. Also, the binarydata 68-2 for the second scan is stored in the buffer 69-2 for thesecond scan, and printed in the second scan by the nozzle array 44(black nozzle array) in the unit area. The image that is printed has aresolution of 600 dpi×600 dpi.

The image processing explained in FIG. 1 is explained in more detailusing FIG. 18. FIG. 18 is an image of a detailed example of the imageprocessing illustrated in FIG. 1. Here, for a resolution of 600 dpi×600dpi, the case of processing image data 140 that corresponds to 4pixels×4 pixels for a total of 16 pixels is correlated with FIG. 1 andexplained. Reference codes A to P represent combinations of RGB valuesof image data 140 that corresponds to each of the 600 dpi×600 dpipixels. In addition, reference codes ae1 to 1 p 1 represent combinationsof CMYK values of multi-value data 141 for the first scan thatcorresponds to each of the 600 dpi×300 dpi pixels, and reference codesae2 to 1 p 2 represent combinations of CMYK values of multi-value data142 for the second scan that corresponds to each of the 600 dpi×300 dpipixels.

In FIG. 18, the multi-value data 140 corresponds to the multi-value RGBdata that is input to the color conversion/image data division unit 62.The multi-value data 141 corresponds to the multi-value data 64-1 forthe first scan as illustrated in FIG. 1, and multi-value data 142corresponds to the multi-value data 64-2 for the second scan. Moreover,the data 143 after quantization (conversion to three values) for thefirst scan corresponds to the quantized data 66-1 for the first scan,and the data 144 after quantization (conversion to three values) for thesecond scan corresponds to the quantized data 66-2 for the second scan.Furthermore, the binary data 145 corresponds to the binary data 68-1 forthe first scan, and the binary data 146 corresponds to the binary data68-2 for the second scan.

The following explanation will be in order of processing. First, thecolor conversion/image division unit 62 converts the 600 dpi×600 dpiinput image data 140 (RGB) to multi-value data 141 (CMYK) for the firstscan and multi-value data 142 (CMYK) for the second scan, each having aresolution designated by the processing resolution setting unit 60. Inthis embodiment, the processing resolution setting unit 60 designates aresolution of 600 dpi×300 dpi, so the multi-value data 141 for the firstscan and the multi-value data 142 for the second scan have a resolutionof 600 dpi×300 dpi.

When doing this, the color conversion/image data division unit 62calculates the average value of the input image data (RGB) among aplurality of pixels corresponding to the resolution designated by theprocessing resolution setting unit 60. Here, when the designatedresolution is 600 dpi×300 dpi as in this embodiment, the colorconversion/image data division unit 62 calculates the average value ofinput image data (RGB) among two adjacent pixels in the verticaldirection (sub scanning direction) in the pixels arranged 600 dpi×600dpi. In other words, in the case of the image data 190 at the upper leftin FIG. 18, the average value Ave (A, E) of A and E is calculated foreach of the three values RGB. After that, by referencing a 3-dimensionalLUT that is prepared in advance, the color conversion/image datadivision unit 62 converts the data to four values (CMYK) that correspondto these three values (RGB), or in other words, converts the data tomulti-value data (ae1) for the first scan and multi-value data (ae2) forthe second scan.

Moreover, as a different method, a 3-dimensional LUT is referenced for a600 dpi×600 dpi resolution as is, and (CMYK) having a 600 dpi×600 dpiresolution can be converted first to two divisions. In this case, forthe two groups of obtained 600 dpi×600 dpi CMYK values, the averagevalue is calculated among a plurality of pixels corresponding to thedesignated resolution and taken to be the multi-value data for the firstscan (ae1) and the multi-value data for the second scan (ae2). In otherwords, the averaging process based on the resolution designated by theprocessing resolution setting unit 60 can be performed before the colorconversion process of converting from RGB to CMYK, or can be performedafter the color conversion process.

The following processing is performed independently and simultaneouslyfor each color CMYK, so for convenience, the following explanation willbe for only one color (for example, black (K)), and an explanation ofthe other colors will be omitted.

The multi-value data (141) for the first scan is input to thequantization processing unit 65-1 where it undergoes multi-valueerror-diffusion processing and is converted to quantized data (143) forthe first scan. Moreover, the multi-value data (142) for the second scanis input to the quantization processing unit 65-2 where it undergoesmulti-value error-diffusion processing and is converted to quantizeddata (144) for the second scan. When doing this, error-diffusionprocessing is performed by the quantization processing unit 65-1 usingthe error-diffusion matrix A illustrated in FIG. 7A, and error-diffusionprocessing is performed by the quantization processing unit 65-2 usingthe error-diffusion matrix B illustrated in FIG. 7B. In the case of thisembodiment, the quantized data 143 and 144 that is obtained in this wayhas resolution of 600 dpi×300 dpi, and each pixel is expressed by threevalues, 0 to 2.

After that, the quantized data 143 undergoes first scan index expansionprocessing and is converted to binary data (145) for the first scan.Quantized data 144 also undergoes second scan index expansion processingand is converted to binary data (146) for the second scan. Morespecifically, by referencing the dot arrangement pattern explained usingFIG. 12, 600 dpi×300 dpi 3-value data that is expressed by 0 to 2 isconverted to 600 dpi×600 dpi binary data.

For examples of binary data 145 and 146, the data of each pixel that is“1” is data for which a dot is printed (ink is discharged), and datathat is “0” is data for which a dot is not printed (no ink isdischarged). In other words, in binary data 145, for a sub pixel that is“1”, a dot is printed in the first printing scan, and in binary data146, for a sub pixel that is “1”, a dot is printed in the secondprinting scan. By doing so, for a sub pixel that is “1” and surroundedby a circle, a dot is printed in the first printing scan and secondprinting scan such that the dots overlap, and for a sub pixel that is“1” and is not surrounded by a circle, a dot is printed in either thefirst printing scan or second printing scan, and dots are notoverlapped. Therefore, it is possible to have overlapping dots andnon-overlapping dots suitably coexist in the image, so it is possible tosuppress density fluctuation even when there is deviation in theprinting position between the first scan and second scan.

As explained above, with this embodiment, by dividing multi-value imagedata into data for a first scan and second scan and performingquantization processing, non-overlapping dots and overlapping dots aresuitably mixed, and it becomes possible to output an image for whichdensity fluctuation and density unevenness has been suppressed. Inaddition, when doing this, by making the resolution before quantizationprocessing temporarily lower than the input multi-value data, the numberof pixels that become the object of the quantization processing (or inother words, the number of times quantization is performed) can be keptfrom being increased more than necessary. That is, with this embodiment,in a series of image processing, it is possible to output a high qualityimage for which density fluctuation has been suppressed and with adecrease in processing speed. Furthermore, by taking the quantizationprocess above to be multi-value quantization processing, and usedtogether with dot arrangement pattern processing, the printingresolution can be equivalently returned to the input resolution, with nodrop in the resolution.

An example of 2-pass multi-pass printing has been explained above,however, it is also possible of course for this embodiment to correspondto an even larger number of passes. In this case, the colorconversion/image data division unit 62 divides the image data that hasbeen converted to low resolution into M number of planes that correspondto M number of multipasses, and quantization processing is executed foreach of the M number of planes.

However, the method of performing the quantization process afterdividing the data into a plurality of planes as in Japanese PatentLaid-Open No. 2000-103088 and the present invention is particularlyeffective in reducing density unevenness in multipass printing having asmall number of passes (low-pass printing) such as two passes asdescribed above. That is because the lower the number of passes, thefewer number of planes there are in which printing is performed over thesame area, and deviation of the printing position of one plane has alarge effect on the image density. On the other hand, in multipassprinting with a large number of passes, there is a large number ofplanes in which printing is performed over the same area, so even thoughdeviation of the printing position occurs in one or two planes, there isnot so much of an effect on the image density, and density unevennessdue to deviation of the printing position is not as much of a problem asin low-pass printing.

Moreover, in low-pass printing, high-speed image output is oftendesired, so that this embodiment, in which the processing load ofquantization is reduced, is able to have an effect on both the reductionof density unevenness and an improvement of processing speed in low-passprinting. On the other hand, in many pass-printing in which high-qualityimage output is often desired, there is a possibility that image qualitywill decrease due to the process described above for lowering theresolution. In the process for lowering the resolution, the originaldetailed image information of the pixels is lost due to unification ofthe multi-value data of a plurality of adjacent pixels, so after that,even when returning to the original resolution in the index expansionprocess, the lost information does not completely return.

Therefore, in consideration of the characteristics of the imageprocessing of this embodiment described above, a plurality of printingmodes having different number of multipasses are prepared for theprinter of this embodiment, and using a different image processingmethod depending on the set printing mode is effective. For example,when the printer is set to the high-speed mode (first mode), after theprocess for lowering the resolution and the division process fordividing the data into M planes, quantization processing is performedfor each plane to generate first quantized data. After that, an image isprinted by M number (M is an integer 2 or greater) of relative movements(M-pass printing) according to the M number of first quantized data. Onthe other hand, when the printer is set to the high-quality mode (secondmode), the input image data is binarized as is using the conventionalmethod and the and second quantized data are generated withoutperforming the resolution reduction process and division process. Thissecond quantized data is divided into N number of data using a maskpattern that is used in a conventional method, and an image is printedby N number (N>M) of relative movements (N-pass printing). By doing soit is possible to obtain both high-speed output with no densityunevenness by using low-pass printing (M-pass printing), and output ahigh-quality image by using many-pass printing (N-pass printing).

In addition, when the printer is set to the high-quality mode (secondmode), it is possible to divide the input image data into M planeswithout processing for lowering the resolution. That is, after dividingthe input image data into M planes without processing for lowering theresolution the error diffusion processing is executed for each of the Mnumber of planes to generate binary data. By doing this, an effects ofthe density fluctuation can be reduced in the high-quality mode (secondmode).

Embodiment 2

In the following, a second embodiment of the present invention will beexplained. Generally, in a highlighted portion where graininess isnoticeable, it is preferred to evenly disperse the few number of dots(1701, 1702) such that they have a fixed distance between them asillustrated in FIG. 8B. Moreover, in high-density portion where thehighest density values are important, it is preferred that dots befilled in to an extent that there are no exposed areas of blank paper.In other words, it is desired that the ratio of areas of overlappingdots (dot overlap rate) be adjusted with good balance within a rangesuch that density unevenness, graininess and insufficient density of theoutput image are not a problem.

However, in the method disclosed in Japanese Patent Laid-Open No.2000-103088, quantization processing is performed for each plane withoutany correlation among the plurality of planes, and the dot overlap rateis set such that it depends on the quantization processing method used.In other words, in the method disclosed in Japanese Patent Laid-Open No.2000-103088, it was possible to set the dot overlap rate such that itwas not 0, however; it was not possible to adjust the dot overlap ratewithin a desired range.

For example, in the construction disclosed in Japanese Patent Laid-OpenNo. 2000-103088, locations (1603) where dots overlap, and adjacentprinted locations (1601, 1602) occur here and there as illustrated inFIG. 8C, so clumps of these dots stand out and cause graininess tobecome worse. In addition, in high-density areas where maximum densityvalues are important, blank areas may become exposed due to overlappingof dots, and this may cause insufficient density. As a result, it isdifficult to output an image at high speed in which there is no problemwith density unevenness, graininess and insufficient density in any ofthe density portions.

In order that this embodiment can handle new problems such as this inaddition to the problems that the invention is to solve as explainedabove, an image processor that is constructed in order to more activelyadjust the dot overlap rate of dots that are printed by different planes(printing scanning) is explained.

Here, the term “dot overlap rate’ as used in this specification will beexplained. “Dot overlap”, as illustrated in FIGS. 4A to 4H and FIG. 10,is the ratio of the number of dots (overlapping dots) that are to beprinted in the same location by different printing scans or differentprinting element groups to the total number of dots to be printed perunit area of K (K is an integer 1 or greater) number of pixels. The samelocation in the case of FIGS. 9A to 4G is the same pixel location, andin the case of FIG. 10 is the sub pixel location.

Using FIGS. 4A to 4H, the dot overlap rate for a first plane and secondplane that correspond to a unit area comprising 4 pixels (main scanningdirection)×3 pixels (sub scanning direction) is explained. The “firstplane” is a collection of binary data that correspond to the first scanor first nozzle group, and the “second plane” is a collection of binarydata that correspond to the second scan or second nozzle group.Moreover, “1” represents data that indicates that a dot will be printed,and “0” represents data that indicates that a dot will not be printed.

In FIGS. 4A to 4E, the number of “1s” in the first plane is “4” and thenumber of “1s” in the second plane is also “4”, so the total number ofdots to be printed in a unit area comprising 4 pixels×3 pixels is “8”.On the other hand, the number of “1s” in the first plane and secondplane that correspond to the same pixel location is the number of dots(overlapping dots) that is printed in the same pixel such that theyoverlap. According to this definition, the number of overlapping dots inthe case of FIG. 4A is “0”, in the case of FIG. 4B is “2”, in the caseof FIG. 4C is “4”, in the case of FIG. 4D is “6” and in the case of FIG.4E is “8”. Therefore, as illustrated in FIG. 4H, the dot overlap ratesin FIGS. 4A to 4E are, 0%, 25%, 50%, 75% and 100%, respectively.

Furthermore, FIGS. 4F and 4G illustrate cases in which the number ofprinted dots in a plane and number of total dots differ from the casesof FIGS. 4A to 4E. FIG. 4F illustrates the case in which the number ofdots printed in the first plane is “4”, the number of dots printed inthe second plane is “3”, the total number of dots is “7”, the number ofoverlapping dots is “6” and the dot overlap rate is 86%. On the otherhand, FIG. 4G illustrates the case in which the number of dots printedin the first plane is “4”, the number of dots printed in the secondplane is “2”, the total number of dots is “6”, the number of overlappingdots is “2 and the dot overlap rate 33%.

In this way, the term “dot overlap rate” in this specification is theoverlap rate of dot data when dot data corresponding to different scansor different printing element groups overlap virtually.

The image processing method of the present invention for controlling thedot overlap rate is explained in detail. In this embodiment, asillustrated in FIG. 11B, a printing head 5004 is used that comprises twonozzle arrays (print element groups) for each color. In the figure, 51and 58 are cyan nozzle arrays, 52 and 57 are magenta nozzle arrays, 53and 56 are yellow nozzle arrays and 54 and 55 are black nozzle arrays.By arranging the nozzle arrays for each color such that they aresymmetric in the main scanning direction as in this example, it ispossible to fix the order of ink application to the print medium of theprinting scan in the forward direction and of the printing scan in thebackward direction. In this embodiment, 2-pass multipass printing isexecuted using two nozzle arrays for one color such as this.

FIG. 14 is a block diagram for explaining the steps of the imageprocessing that is executed in this embodiment. In this embodiment aswell, RGB multi-value image data that is input from an external deviceto the multi-value image data input unit 71 is such that individualpixels for each color is expressed by 8-bit (256 values) and has a 600dpi×600 dpi resolution. In addition, the color conversion/image datadivision unit 72 converts this input image data (256-value RGB data) totwo sets of multi-value image data (256-value density data) thatcorrespond to the ink colors (CMYK). However, in the colorconversion/image data division unit 72, with bias being appliedaccording to a specified distribution rate, the image data is dividedinto image data for the first scan and image data for the second scan. Afeature of this embodiment is controlling the dot overlap rate byadjusting the distribution rate of the color conversion/image datadivision unit 72 in this way. The relationship between the distributionrate and dot overlap rate will be explained in detail later.

In this embodiment as well, the processing resolution setting unit 71sets the resolution of the image data after division by the colorconversion/image data division unit 72. For example, when the processingresolution setting unit 70 designates a resolution of 600 dpi×300 dpi,the color conversion/image data division unit 62 output two groups of256-value density data that corresponds to the ink colors (CMYK)according to a specified distribution rate and with a resolution of 600dpi×300 dpi. As a result of performing this kind of process, it ispossible to complete the gradation correction process and quantizationprocess by performing processing the same number of times as theconventional method in which the division process is not performed (themethod disclosed in Japanese Patent Laid-Open No. 2000-103088 is notemployed) the same as in the first embodiment.

The processing described below is performed independently andsimultaneously for each of the colors CMYK, so the following explanationwill be for just the color black (K). In the color conversion/image datadivision unit 72, multi-value data for the first scan and multi-valuedata for the second scan that are generated according to a specifieddistribution rate undergo a gradation correction process as in the firstembodiment by the gradation correction units 73-1 and 73-2,respectively. After that, as in the first embodiment, the quantizationprocessing units (75-1 and 75-2) perform quantization processing andsend the data to the printer engine 3004 via an IEEE 1284 bus 3022. Theprinter engine 3004, then executes the following processing.

In the printer engine 3004, 3-value data 76-1 for the first scan, and3-value data 76-2 for the second scan undergo index expansion processingas in the first embodiment explained in FIG. 12. By this processing, the3-value data 76-1 and 76-2 are converted to 600 dpi×600 dpi binary data78-1 and 78-2 that is expressed by two values of 1-bit.

After that, the binary data 78-1 is input to the first scan binary datadivision processing unit 79-1 and divided into binary data 80-1 for thefirst nozzle array in the first scan, and binary data 80-2 for thesecond nozzle array in the first scan. Moreover, the binary data 78-2 isinput to the second scan binary data division processing unit 79-2 anddivided into binary data 80-3 for the first nozzle array in the secondscan, and binary data 80-4 for the second nozzle array in the secondscan. In this embodiment, in the first scan binary data divisionprocessing unit 79-1 and second scan binary data division processingunit 79-2, the division processing is executed using masks that arestored in memory in advance. A mask is a collection of data which setpermitting to print (1) or not permitting to print (0) for each binaryimage data of the 600 dpi×600 dpi pixels, and by performing a logicalAND operation between the mask and the binary image data for each pixelthe binary data is divided.

In the case where the binary image data are divide into N divisions,normally N number of masks are used, and in this embodiment where thebinary image data are divided into two divisions, two masks 1801 and1802 as illustrated in FIG. 5 are used. Here, mask 1801 is used forgenerating binary data for the first nozzle array, and mask 1802 is usedfor generating binary data for the second nozzle array. These two maskshave a complementary relationship with each other, so the binary datathat are divided using these masks will not overlap each other.Therefore, compared with the two planes that were divided out by thecolor conversion/image data division unit 72, a plane relationshipoccurs in which it is more difficult for graininess to become worse andfor insufficient density to occur. In FIG. 5, the black areas are data(1: data for which the image data is not masked) for which printingimage data is permitted, and white areas are data (0: data for which theimage data is masked) for which printing image data is not permitted. Inthis embodiment, the same set of masks 1801 and 1802 are used by thefirst scan binary data division processing unit 79-1 and second scanbinary data division processing unit 79-2. However, as long as the masksfor the first nozzle array and second nozzle array have a complementaryrelationship with each other, it is also possible to use a different setof masks for the first scan and second scan.

After that, the binary data (80-1) for the first nozzle array in thefirst scan is stored in a buffer (81-1) for the first nozzle array inthe first scan, and printed in a unit area in the first scan by nozzlearray 54. The binary data (80-2) for the second nozzle array in thefirst scan is stored in a buffer (81-2) for the second nozzle array inthe first scan, and printed in a unit area in the first scan by nozzlearray 55. The binary data (80-3) for the first nozzle array in thesecond scan is stored in a buffer (81-3) for the first nozzle array inthe second scan, and printed in a unit area in the second scan by nozzlearray 54. Furthermore, the binary data (80-4) for the second nozzlearray in the second scan is stored in a buffer (81-4) for the secondnozzle array in the second scan, and printed in a unit area in thesecond scan by nozzle array 55. The printed image has a resolution of600 dpi×600 dpi.

The method and effect of adjusting the distribution rate for controllingthe dot overlap rate is explained below. Table 1 gives the distributionrates for the multi-value data for the first scan and second scan by thecolor conversion/image data division processing unit 72 of thisembodiment, and dot overlap rates of the first scan and second scan whentypical error diffusion processing is performed on the multi-value data.

The printing rate (%) in Table 1 corresponds to the number of dots ofone color of ink that is printed per unit area, where 0% is the state inwhich no dots are printed per unit area, and 100% is the state in whichthe maximum number of dots is printed per unit area. Therefore, forexample, a printing rate of 60% indicates a state in which the number ofdots printed per unit area corresponds to a value (153) that is 60% themaximum value (255) of multi-value data K that is input to the colorconversion/image data division unit 72. In Table 1, this printing rateis given in 10 levels from 0 to 100%.

Moreover, the distribution rate (%) is the ratio of the multi-value dataset according to the printing rate that is distributed to the first scan(K1) and the second scan (K2), where the total distribution rate is100%. For example, when distributing the multi-value data value (K=100)to multi-vale data (K1=80) for the first scan, and multi-value data(K2=20) for the second scan, the distribution rate is (K1:K2=80:20). InTable 1, this kind of distribution rate is given in 6 levels. The dotoverlap rates, which are the result of quantization processing by thetypical error-diffusion method and the index expansion processillustrated in FIG. 12, are given in each column corresponding to thedistribution rate and printing rate.

TABLE 1 Distribution rate (%) Printing rate (%) First scan Second scan10 20 30 40 50 60 70 80 90 100 100 0 0 0 0 0 0 0 0 0 0 0 90 10 1.8 3.65.4 7.2 9 10.8 12.6 14.4 16.2 18 80 20 3.2 6.4 9.6 12.8 16 19.2 2.4 25.628.8 32 70 30 4.2 8.4 12.6 16.8 21 25.2 29.4 33.6 37.8 42 60 40 4.8 9.614.4 19.2 24 28.8 33.6 38.4 43.2 48 50 50 5 10 15 20 25 30 35 40 45 50

FIG. 6 is a diagram that illustrates Table 1 as a graph. The horizontalaxis is the printing rate, the vertical axis is the dot overlap rate,and for each of the 6 levels of distribution rates illustrated in Table1, the dot overlap rate with respect to the printing rate is expressedas a straight line with a different slope. For example, when thedistribution rate for the first printing scan is 100% and thedistribution rate for the second printing scan is 0%, all of themulti-value data is printed by just the first printing scan. In thiscase, there is no dot overlap, and even though the printing rateincreases the dot overlap rate remains at 0%. As the distribution ratefor the second printing scan gradually increases, the slope of the dotoverlap rate with respect to the printing rate gradually increases. Inaddition, when both the distribution rate for the first printing scanand second printing scan is 50%, the slope of the dot overlap rate withrespect to the printing rate becomes a maximum, and when the printingrate is 100%, the dot overlap rate becomes 50%. Therefore, by obtainingthe relationship between the distribution rate and dot overlap rate inadvance as illustrated in Table 1 and FIG. 6, it is possible to achievethe desired dot overlap rate by adjusting the distribution rate.

In FIG. 6, the thick line 311 illustrates the state in this embodimentof adjusting the dot overlap rate according to the printing rate (or inother words the total value of a plurality of multi-value density datacorresponding to different scans). In this embodiment, in low-densityportions where the printing rate is up to 20%, the dot overlap rate is0%, in medium density portions where the printing rate is 20 to 60%, thedot overlap rate gradually increases to 30%, and in high-densityportions where the printing rate is 60% or greater, the dot overlap rategradually drops to 20% or less. In order to achieve this kind of dotoverlap rate, the distribution rate at a printing rate of 0 to 20% is(100%:0%), and at a printing rate of 20 to 60%, the distribution rate isgradually changed until it becomes (50%:50%). In addition, at a printingrate of 60%, in order that the dot overlap rate becomes a maximum, thedistribution rate is made to be (50%:50%). Moreover, in high-densityareas where the printing rate is 60 to 100%, the distribution rate isgradually changed unit it becomes (90%:10%). In this embodiment, thedistribution rate is set in this way such that the dot overlap rate inmedium-density portions, where density unevenness due to densityfluctuation caused by deviation of the printing position is consideredto be the most important, is higher than in low-density portions andhigh-density portions. In order to suppress the occurrence of pseudocontours, it is preferred that adjustment of the distribution rate bechanged as smoothly as possible with respect to change in the printingrate.

Incidentally, in this embodiment, the color conversion/image datadivision unit 62 converts all of the input image data (RGB) together toa plurality of multi-value density data corresponding to the printingscans, so parameters such as those that correspond to the “printingrates” illustrated in Table 1 and FIG. 6 are not actually used. However,there is a correlation between the total value of multi-value data forthe first printing scan and multi-value data for the second printingscan after distribution and the printing rate, and when this total valuebecomes large, the printing rate after binarization becomes large. Inother words, the total value of a plurality of multi-value density datathat corresponds to different scans corresponds to the “printing rate”.Therefore, in actual processing, RGB coordinates can be correlated withCMYK values in a 3-dimensional LUT so that the multi-value data at thecoordinates where the total value of multi-value data for each printingscan corresponds to a printing rate of 60% is distributed for eachprinting scans at the distribution rate of (50:50). In other words, inthis embodiment, the color conversion/image data division unit 72performs data conversion by using a LUT table in which the RGBcoordinates are correlated with CMYK multi-value data so that therelationship between the total value of multi-value data for eachprinting scan (printing rate) and the distribution rate satisfies thegraph indicated by the thick line in FIG. 6. By doing so, it is possibleto set the dot overlap rate for medium-density portions, where densityunevenness is considered to be the greatest, higher than low-densityportions and high-density portions, and for all density portions wherethe priority between density unevenness and graininess changes, it ispossible to output a good image.

Also, in this embodiment, as in the first embodiment, the colorconversion/image data division unit 72 does not have to convert all ofthe multi-value brightness data (RGB) to a plurality of multi-valuedensity data (CMYK) at once. The process for converting color from RGBto CMYK can be provided separately from the process of converting CMYKdata to a plurality of multi-value density data that corresponds toprinting. In that case, a plurality of multi-value density data can begenerated according to the distribution rate that is set according tothe multi-value data after color conversion, or in other words,according to Table 1.

The process for lowering the resolution, as in the first embodiment, canbe performed in any stage as long as it is performed before thequantization process. In other words, the color conversion process forconverting RGB to CMYK can be performed in the RGB stage aftercalculating the average value of multi-value data among a plurality ofadjacent pixels, and the process for lowering the resolution can beperformed after the color conversion process.

In Table 1, the color conversion/image data division unit 72 sets thedistribution rates such that the sum of the distributions rates for thefirst printing scan and second printing scan becomes 100%, however; thisembodiment is not limited to this. With the convenience of the imageprocessing or the object of improving the absolute density, the sum ofthe distribution rate for the first printing scan and the distributionrate for the second printing scan can be greater than 100%, or may beless than 100%.

With the embodiment explained above, by performing quantizationprocessing after dividing multi-value density data for a first printingscan and second printing scan according to a suitable distribution rate,it is possible to set the dot overlap rate in density portions wheredensity unevenness is considered to be more of a problem higher than inother portions. When doing this, by making the resolution after divisionlower than that of the input multi-value density data, it is possible tokeep from increasing the number of times quantization processing isperformed more than necessary. Therefore, in a series of imageprocessing, it is possible to output an image for which variousproblems, including density unevenness, are suppressed for all ofdensity portions without lowering the processing speed.

Embodiment 3

In the second embodiment, a method was explained in which the colorconversion/image data division unit adjusts the distribution rate inorder to control the dot overlap rate. In this embodiment, the dotoverlap rate is controlled by providing features to the quantizationprocess when quantizing the plurality of multi-value density data thatis generated by the color conversion/image data division unit. Whendoing this, the dot overlap rate may also be controlled by thequantization processing unit cooperating with adjustment of thedistribution rate by the color conversion/image data division unit.

FIG. 15 is a block diagram for explaining image processing whenperforming multipass printing for completing an image in the same areaof a printing medium by two printing scans. In this embodiment, exceptfor the quantization processing unit 25, the construction is the same asthat of the second embodiment that was explained using FIG. 14.Therefore, only the processing executed by the quantization processingunit 25 will be explained here.

FIG. 9 is a flowchart for explaining processing steps that are executedby the quantization processing unit 25 of this embodiment. In thisflowchart, the two objects to be quantized, or in other words, inputmulti-value data 24-1 for the first scan and input multi-value data 24-2for the second scan are indicated as K1 and K2, respectively, and havevalues 0 to 255. In addition, K1 err and K2 err are accumulated errorvalues that are generated from surrounding pixels for which quantizationprocessing has already been completed, and K1 ttl and K2 ttl are totaledvalues of the input multi-value data (K1, K2) and accumulated errorvalues (K1 err, K2 err). Furthermore, K1′ and K2′ in the flowchartindicate 3-value quantized data for the first printing scan and secondprinting scan.

In this embodiment, threshold values (quantization parameters) that areused when setting the 3-value quantized data K1′ and K2′, differdepending on the values K1 ttl and K2 ttl. For this purpose, the valuesK1 ttl and K2 ttl are taken to be arguments, and a threshold value tableis prepared in advance from which two threshold values, which havedifferent sizes, are selected corresponding to these arguments. Here,when setting K1′, K1table_1[K2 ttl] is a first threshold value forcomparison with K1 ttl, and K1table_2[K2 ttl] is a second thresholdvalue that is larger than the first threshold value. Moreover, whensetting K2′, K2table_1[K1 ttl] is a first threshold value for comparisonwith K2 ttl, and K2table_2[K1 ttl] is a second threshold value that islarger than the first threshold value. Both K1table_1[K2 ttl] andK1table_2[K2 ttl] are values that are selected from the threshold valuetable with K2 ttl as an argument. Both K2table_1[K1 ttl] andK2table_2[K1 ttl] are values that are selected from the threshold valuetable with K1 ttl as an argument.

When this process is started, first, in step S21 K1 ttl and K2 ttl arecalculated. Next, in step S22, by referencing the threshold value table,the four threshold values are obtained from K1 ttl and K2 ttl that werecalculated in step S21. The threshold values K1table_1[K2 ttl] andK1table_(—2)[K2 ttl] are primarily set by referencing the table with K2ttl as an argument. Also, the threshold values K1table_2[K1 ttl] andK2table_2[K1 ttl] are primarily set by referencing the table with K1 ttlas an argument.

Next, in steps S23 to S26, the value K1′ is set, and in steps S27 toS30, the value K2′ is set. More specifically, in step S23, the value K1ttl that was calculated in step S21 is compared with the thresholdvalues K1table_1[K2 ttl] and K1table_2[K2 ttl] that were obtained instep S22. When it is determined that K1 ttl<K1table_1[K2 ttl], thenK1′=0, and the accumulated error value K1 err (=K1 ttl) is updatedaccording to this output value (K1′=0) (step S24). Moreover, when it isdetermined that K1table_1[K2 ttl]≦K1 ttl≦K1table_2[K2 ttl], then K1′=1,and the accumulated error value K1 err (=K1 ttl−128) is calculatedaccording to this output value (K1′=1) and updated (step S25).Furthermore, when it is determined that K1table_2 [K2 ttl]<K1 ttl, thenK1′=2, and the accumulated error value K1 err (=K1 ttl−255) iscalculated according to this output value (K1′=2) and updated (stepS26).

Next, in step S27, the value K1 tt 2 that was calculated in step S21 iscompared with the threshold values K2table_1[K1 ttl] and K2table_2[K1ttl] that were obtained in step S22. When it is determined that K2ttl<K2table₁[K1 ttl], then K2′=0, and the accumulated error value K2 err(=K2 ttl) is updated according to this output value (K2′=0) (step S28).Moreover, when it is determined that K2table_1[K1 ttl]≦K2 ttl≦K2table_2[K1 ttl], then K2′=1, and the accumulated error value K2 err (=K2ttl−128) is calculated according to this output value (K2′=1) andupdated (step S25). Furthermore, when it is determined thatK2table_(—2[K1) ttl]<K2 ttl, then K2′=2, and the accumulated error valueK2 err (=K2 ttl−255) is calculated and updated according to this outputvalue (K2′=2) (step S30).

After that, in step S31, the accumulated error values K1 err and K2 errthat were updated in this way are diffused to the surrounding pixels forwhich quantization has not yet been completed according to theerror-diffusion matrix illustrated in FIG. 7A or FIG. 7B. In thisembodiment, the error-diffusion matrix illustrated in FIG. 7A is usedfor diffusing the accumulated error K1 err to the surrounding pixels,and the error-diffusion matrix illustrated in FIG. 7B is used fordiffusing the accumulated error K2 err to the surrounding pixels.

In this embodiment, the two threshold values (quantization parameters)that are used for performing the quantization process on the firstmulti-value data (K1 ttl) that corresponds to the first scan are setbased on the second multi-value data (K1 ttl) that corresponds to thesecond scan. Similarly, the two threshold values (quantizationparameters) that are used for performing the quantization process on thesecond multi-value data (K2 ttl) that corresponds to the second scan areset based on the first multi-value data (K1 ttl) that corresponds to thefirst scan. In other words, the quantization process of multi-value datathat corresponds to one scan of two scans, and the quantization processof multi-value data that corresponds to the other scan of two scans areboth executed based on the multi-value data that corresponds to the onescan and the multi-value data that corresponds to the other scan. Inthis way, for example, the table contents can be adjusted in advance sothat dots that are printed in one scan are as much as possible notprinted in the pixels in which dots are printed in the other scan, orvice versa. As a result, it is possible to increase the suppression ofdensity unevenness according to gradation, while at the same time keep abalance between worsening graininess and insufficient density.

FIG. 13 is a diagram for explaining the correlation between an exampleof the results from performing quantization processing (binarizationprocessing) using threshold values that are given in a specifiedthreshold value table according to the flowchart in FIG. 9 and the inputvalues (K1 ttl and K2 ttl). Both K1 ttl and K2 ttl take on values 0 to255, and depending on the combinations of these, K1′ and K2′ are set asillustrated in the figure to 2-dot printing (2), 1-dot printing (1) orno printing (0). Here, the first threshold value K2table_1[K1 ttl] thatis used for quantization of K2 ttl is indicated by the bold dotted line,and the second threshold value K2table_2[K1 ttl] is indicated by thebold dashed line. For example, for a pixel in which both K1′ and K2′become 2, that is, for a pixel corresponding to the upper right area ofthe figure, two dots are printed in 1×2 sub pixels in the first printingscan and second printing scan respectively. When K1′ is 1 and K2′ is 2,or in other words, in a pixel that corresponds to the area on the rightside of the figure, 1 dot is printed in a 1×2 sub pixel in the firstprinting scan, and two dots are printed in a 1×2 sub pixel in the secondprinting scan. When both K1′ and K2′ are 0, or in other words, in apixel that corresponds to the area at lower left of the figure, no dotsare printed in either the first scan or second scan.

In this embodiment, a table is prepared in this way such that thethreshold values change according to the values K1 ttl and K2 ttl, or inother words, a table is prepared for setting two threshold values forcomparison with K2 ttl (or K1 ttl), using K1 ttl (or K2 ttl) as anargument. By doing this, as illustrated in FIG. 13, it is possible tochange the threshold values for comparison with K2 ttl (or K1 ttl)according K1 ttl (or K2 ttl), and as a result, it is possible to controlthe dot overlap rate in 1×2 sub pixels.

It is also possible to prepare a plurality of kinds of threshold valuetables in advance in order to obtain various results in addition to theresults illustrated in FIG. 13, and by doing so, it is possible toobtain a suitable dot overlap rate according to various printingconditions such as the type of printing medium. As a result, it ispossible to print good images on various kinds of printing media, forwhich problems in the image due to graininess, insufficient density anddensity unevenness have been suppressed in all density portions fromlow-density areas to high-density portions.

In the explanation above, the case of preparing a threshold table fromwhich threshold values for quantization can be selected from arguments(K1 ttl, K2 ttl) was explained, however, the quantization method is notlimited to the method described above. Quantization does not have to besuch that output values (0 to 2) are set by comparison with thresholdvalues. For example, in the case of two planes, a table can be preparedthat primarily sets the values K1′ and K2′ by using both K1 ttl and K2ttl as reference values. The details of such a table are omitted here,however, using a multi-dimensional table such as this has merits in thatthe control is more simple, and the dot overlap rate can be controlledwith a higher degree of freedom. On the other hand, using a1-dimensional threshold value table such as described above has meritsin that it is possible to create a table that requires less memoryspace. It is also possible to use a 1-dimensional threshold value tablethat uses the sum of K1 ttl and K2 ttl as an argument. Furthermore, itis also possible to perform quantization processing by just performingbranching and calculations without using a table at all. In that case,it is possible to obtain the effect of this embodiment by setting thecoefficients that are used in the operations to values that make itpossible to achieve the desired dot overlap rate. In such a case, it ispossible to further reduce the amount of required memory space (size ofROM or RAM used) when compared with the case of preparing the tabledescribed above.

With the embodiment as explained above, quantization processing for eachscan is performed according to multi-value data of each scan afterdividing multi-value density data into data for a first scan and secondscan. By doing so, it is possible to set the dot overlap rate higher indensity portions where density unevenness is considered to be more of aproblem than in other portions. When doing this, by making theresolution after this division process lower than that of the inputmulti-value density data, it is possible to prevent having to increasemore than necessary the number of times quantization processing isperformed. Therefore, in a series of image processing, it is possible tooutput an image for which various problems, including densityunevenness, have been suppressed for all of density portions without adecrease in processing speed.

Other Embodiments

In the first through third embodiments, the case was explained in whichprocessing is performed by lowering the resolution (600 dpi×300 dpi) injust the sub scanning direction with respect to the resolution (600dpi×600 dpi) of the image that is input to the multi-value image datainput unit. However, the degree to which the resolution is lowered canbe changed in various ways according to a setting from the processingresolution setting unit. For example, the resolution (600 dpi×600 dpi)could be lowered in just the main scanning direction (300 dpi×600 dpi),or could be lowered in both the main scanning direction and sub scanningdirection (300 dpi×300 dpi).

When the resolution is lowered in just the sub scanning direction as inthe embodiments described above, an index pattern that is long in thesub scanning direction as illustrated in FIG. 12 is used. By using thiskind of index pattern, it is possible to obtain an image that isresistant to a deviation in the printing position in the main scanningdirection generally. On the other hand, when the resolution is loweredin just the main scanning direction such that the resolution is changedfrom (600 dpi×600 dpi) to (300 dpi×600 dpi), a dot arrangement patternthat is long in the main scanning direction is used as illustrated inFIG. 17. By using this kind of dot arrangement pattern, it is possibleto obtain an image that is resistant to a deviation in the printingposition in the sub scanning direction generally. The load on thequantization process itself is nearly the same whether the resolution islowered in the vertical or horizontal direction. Therefore, theprocessing resolution setting unit can set the processing resolutionaccording to the direction in which it is desired to further reduce theprint deviation.

Moreover, when the color conversion/image data division unit lowers theresolution from (600 dpi×600 dpi) to (300 dpi×300 dpi), for example, thenumber of pixels that become the object of quantization processing iskept at ¼(=½×½) that of when the resolution is not lowered. In thiscase, one 300 dpi×300 dpi pixel corresponds to four 600 dpi×600 dpi subpixels, so in the quantization process, quantization to five values 0 to4 may be performed.

FIG. 16 is a diagram illustrating one example of a dot arrangementpattern that is used in the index expansion process. The left side ofthe figure illustrates pixels having 5 level values that are input tothe index expansion process, and have one of the levels 0 to 4. On theother hand, the right side of the figure illustrates dot arrangementpatterns for 2×2 sub pixels that are selected to correspond to therespective levels. When the level is 0, no dots are printed in any ofthe 2×2 sub pixels, however, as the level increases, then number of dotsprinted increases by one. In level 1 to level 3, a plurality of patternshaving different dot arrangements are prepared, and these can be usedsequentially or can be used selectively according to conditions. Thiskind of resolution reduction and index expansion processing can beapplied to any of the embodiments 1 to 3.

The number of levels after quantization in the quantization process doesnot absolutely need to correspond to the number of sub pixels. Forexample, even though the resolution is lowered from (600 dpi×600 dpi) to(300 dpi×300 dpi), in the quantization process, quantization can beperformed to three values instead of five values. In that case, the dotarrangement patterns that correspond to the levels could be for example,0 dots in level 0, 2 dots in level 1, and 4 dots in level 3.

Control of the dot overlap rate that was made possible in the second andthird embodiments can be made possible by using the index expansionprocess as explained in FIG. 10. FIG. 10 is schematic diagram forexplaining the relationship between 3-value quantized data and the dotarrangement pattern that is converted by the index expansion processingunit in accordance to the first scan and second scan. The left side ofthe figure illustrates pixels having levels of three values that areinput to the index expansion processing unit 27-1 or 27-2, with eachpixel having a value 0 to 2. Each pixel has a resolution of 300 dpi×300dpi, which corresponds to 2×2 sub pixels having a resolution of 600dpi×600 dpi. On the other hand, the center columns in the figureillustrate dot arrangement patterns of the 600 dpi×600 dpi 2×2 subpixels that are selected according to the respective level. The dotarrangement pattern that corresponds to K1′ is the dot arrangementpattern for the first scan, and the dot arrangement pattern thatcorresponds to K2′ is the dot arrangement pattern for the second scan.In the figure, the sub pixels that are indicated by diagonal linesindicate that one dot is printed in that sub pixels during the specifiedscan.

The right side of the figure illustrates the sum of the dot arrangementpattern for the first scan and the dot arrangement pattern for thesecond scan (dot overlap state) that is set in thus way, and the overlaprate for each respective case. In the figure, sub pixels for which nodots are printed in either the first scan or second scan are illustratedas empty, and sub pixels for which one dot is printed in either thefirst scan or second scan are illustrated using diagonal lines.Furthermore, sub pixels for which one dot is printed in both the firstscan and second scan for a total of two overlapping dots are illustratedby a solid black. In this way, it is possible to set the dot arrangementfor the dot arrangement pattern in advance so that the desired dotoverlap rate is obtained. In addition, control of the dot overlap ratethat uses this kind of index expansion processing can be performedtogether with control of the dot overlap rate by a different method suchas that used in the first embodiment of course, as well at that used inthe second and third embodiments.

When the resolution is lowered from (600 dpi×600 dpi) to (300 dpi×300dpi) as described above, the number of pixels that become the object ofthe quantization process becomes approximately ¼ that when theresolution is not lowered. In other words, in 4-pass multipass printing,when divided into four planes, the number of pixels that are the objectof processing can be made to be nearly the same (4×¼=1) as the case inwhich division processing is not performed. In addition, in 2-passmultipass printing, when divided into two planes, the number of pixelscan be made to be ½ (2×¼=½) that of the case in which divisionprocessing is not performed, and thus even faster processing can beexpected. Generally, when performing M-pass printing (M is an integer 2or greater), by making the processing resolution 1/m times in the mainscanning direction and 1/n times in the sub scanning direction such thatm×n=M is satisfied, it is possible to perform the quantization processwith the same load as when the division process was not performed eventhough the division process was performed to divide the data into Mplanes. However, the present invention is not limited to lowering theresolution so that m×n=M is satisfied. In image construction in whichthe quantization process is performed after dividing the data into aplurality of planes, as long as the image is constructed by performingthe quantization process after lowering the resolution to a resolutionthat is lower than the input resolution, it is possible to obtain theeffect of the present invention of reducing the processing load thataccompanies dividing the data. In this case, in index expansion afterthe quantization process, the resolution can be expanded to a resolutionthat is higher than the input resolution (increased resolution).

However, when lowering the resolution, the original detailed imageinformation of pixels is lost due to making the image data in aplurality of adjacent pixels uniform, so after that, even though theoriginal resolution is restored by index expansion processing, the lostinformation is not completely restored. Therefore, when the amount ofresolution reduction (values of m and n) is very large, a decrease inimage quality will stand out. In consideration of this, the resolutionset by the processing resolution setting unit, or in other words, theamount of resolution reduction is preferably set to a suitable valuethat balances the number of division planes, the processing load, therequired processing speed, and the image quality.

In the embodiments described above, the case was explained in which thecolor conversion/image data division unit converts the multi-valuebrightness data (RGB) to a plurality of multi-value density data (CMYK)corresponding to the printing scans in one step by using a 3-dimensionalLUT. However, the present invention and this embodiment are notabsolutely limited to this kind of construction. For example, theprocess of converting the color from RGB to CMYK and the process ofdividing CMYK to a plurality of multi-value density data thatcorresponds to the printing scans can be independent. In this case, itdoes not matter whether the resolution conversion and the divisionprocess are performed in the RGB state before color conversion, orresolution conversion and the division process are performed in the CMYKstate after color conversion. The resolution conversion process anddivision process could also be separately located before and after thecolor conversion process, where the before and after relationship of theresolution conversion process and division process is not particularlylimited. In either case, in the stage of performing the quantizationprocess, as long as multi-value CMYK data for a plurality of scans inwhich the processing resolution is made to be lower than the inputresolution, it is possible to obtain the effect of the present inventionof reducing the load of the quantization process.

Moreover, in the second and third embodiments, with the presumption thata printing head having two nozzle arrays of each color as illustrated inFIG. 11B will be used, the case was explained in which data was dividedin the multi-value stage into a plane for the first printing scan and aplane for the second printing scan. In addition, after the data for eachscan is converted to binary data by the index expansion process, thatbinary data is divided into data for the first nozzle array and for thesecond nozzle array by using a mask pattern having a complementaryrelationship. This kind of construction is effective when densityunevenness between printing scans stands out more than densityunevenness between nozzle arrays. However, the present invention is notlimited to this kind of construction. When the density unevennessbetween nozzle arrays stands out more than the density unevennessbetween printing scans, and when the deviation in the printing positionbetween nozzle arrays is emphasized more, it is possible to perform thedivision process in the opposite order as described above. In that case,the quantization process and index expansion process can be performedafter performing division in the multi-value state to a plane for thefirst nozzle array and a plane for the second nozzle array, and afterthat, binary data can be divided for the first scan and for the secondscan using a mask pattern.

In the embodiments described above, the case was explained in which fourcolors of ink CMYK were used, however, the number of types of ink colorsthat can be used are not limited to this. Light cyan (Lc), or lightmagenta (Lm) ink could be added to these 4 colors of ink, or specialcolor ink such as red (R) or blue (B) ink could also be added. On theother hand, the present invention could also be applied to a mono-colormode in which only one color of ink is used. Furthermore, the inventioncould also be applied to a monochrome printer as well as a colorprinter.

Moreover, in the embodiments described above, the case of using aprinter having the construction as illustrated in the electrical blockdiagram of FIG. 3 was explained, however; the present invention is notlimited to this kind of construction. For example, the printer controlunit and printer engine unit were explained as each being an independentmodule, however, the control unit and printer engine unit can share thesame ASIC, CPU, ROM and RAM. In addition, in the figure, the controlunit and printer engine unit are connected by a USB or IEEE 1284, whichis a general-purpose I/F, however, the present invention could use anyconnection method. Moreover, the connection from the PC takes the formof a direct connection to the printer engine unit via a USB HUB,however, the control unit could also relay the image data. Furthermore,as necessary, the control unit could employ the form of sending imagedata from the PC to the printer engine unit after performing suitableimage processing on the image data.

In the embodiment above, the case was explained in which imageprocessing up to quantization is executed by the control unit 3000, andprocessing after that is executed by the printer engine 3004, however,the present invention is not limited to this kind of construction. Aslong as the series of processes described above are executed, any formof processing method, regardless of the hardware or software, is withinthe scope of the present invention.

Furthermore, in the embodiments described above, using a printer (imageformation device) comprising a control unit 3000 having an imageprocessing function as an example, an image process device that executesimage processing that is characteristic of the present invention wasexplained, however the present invention is not limited to this kind ofconstruction. A construction is possible in which the characteristicimage processing of the present invention is executed by a host devicein which a printer driver is installed (for example PC 3010 in FIG. 3)and image data after quantization processing or division processing isinput to the printer. In such a case, the host (external device) that isconnected to the printer corresponds to the image processor of thepresent invention.

The present invention can also be achieved by program code thatcomprises a program readable by a computer for making possible the imageprocessing functions described above, or a memory medium on which thatprogram code is stored. In this case, the computer (or CPU or MPU) ofthe host device or the image processor make possible the imageprocessing described above by reading and executing the aforementionedprogram code. In order to make the computer execute the image processingdescribed above in this way, the present invention includes a programthat can be read by the computer, or a memory medium on which thatprogram is stored.

It is possible to use, for example, a floppy disk (registeredtrademark), hard disk, optical disk, magnetic optical disk, CD-ROM,CD-R, magnetic tape, non-volatile memory card, ROM and the like as thememory medium for supplying the program code.

Moreover, by the computer reading and executing the program code, notonly is it possible to achieve the functions of the embodimentsdescribed above, but based on the instruction of that program code, theOS operating on the computer can also perform part or all of the actualprocessing. Furthermore, after the program code has been written in thememory of a function expansion board that is inserted into the computer,or a function expansion unit that is connected to the computer, the CPUcan perform part or all of the processing based on the instructions ofthat program.

Aspects of the present invention can also be realized by a computer of asystem or apparatus (or devices such as a CPU or MPU) that reads out andexecutes a program recorded on a memory device to perform the functionsof the above-described embodiment(s), and by a method, the steps ofwhich are performed by a computer of a system or apparatus by, forexample, reading out and executing a program recorded on a memory deviceto perform the functions of the above-described embodiment(s). For thispurpose, the program is provided to the computer for example via anetwork or from a recording medium of various types serving as thememory device (e.g., computer-readable medium).

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2009-235328, filed on Oct. 9, 2009, which is hereby incorporated byreference herein in its entirety.

1. An image processor for processing input image data that correspondsto a pixel area in order to perform printing the pixel area on aprinting medium by a plurality of relative movements of a printing unitfor printing a same color dot, with respect to a printing medium,comprising: a first generation unit configured to generate a pluralityof multi-value data for the same color corresponding to the plurality ofrelative movements, that have a lower resolution than the input imagedata, based on the input image data; a second generation unit configuredto generate a plurality of quantized data corresponding to the pluralityof relative movements by performing quantization processing to each ofthe plurality of multi-value data and to create M number of quantizeddata having a lower number of levels than the multi-value data; and athird generation unit configured to generate a plurality of binary datafor the same color corresponding to the plurality of relative movements,that have higher resolution than the quantized data, by performingbinarization processing to each of the plurality of quantized datacorresponding to the plurality of relative movements.
 2. The imageprocessor according to claim 1, wherein the resolution of the binarydata is equal to the resolution of the input image data.
 3. The imageprocessor according to claim 1, wherein the first generation unitgenerates the multi-value image data having the lower resolution thanthe input image data by performing an averaging process of a pluralityof the input image data corresponding to a plurality of pixel areas. 4.The image processor according to claim 1, wherein the first generationunit generates the multi-value image data having the lower resolutionthan the input image data by performing an averaging process of aplurality of the multi-value image data for the same color correspondingto a plurality of pixel areas.
 5. The image processor according to claim1, wherein the third generation unit generates the binary data having ahigher resolution than the quantized data by referencing a dotarrangement pattern.
 6. An image processor for processing input imagedata that corresponds to a pixel area in order to perform printing inthe pixel area on a printing medium by a plurality of relative movementsof a printing unit for printing a same color dot, with respect to theprinting medium, comprising: a setting unit configured to set one modefrom among a plurality of printing modes that include a first mode forprinting in the pixel area by performing M (where M is an integer largerthan 2) number of relative movements, and a second mode for printing inthe pixel area by performing N (where N is an integer larger than 3 andN>M) number of relative movements; and a processing unit configured to,when the first mode has been set by the setting unit, (A) generate aplurality of multi-value image data for the same color corresponding tothe plurality of relative movements, that have a lower resolution thanthe input image data, based on the input image data, (B) generate aplurality of quantized data corresponding to the plurality of relativemovements, by performing quantization processing to each of theplurality of multi-value image data for the same color corresponding tothe plurality of relative movements, and (C) generate a plurality ofbinary data corresponding to the plurality of relative movements, thathave a higher resolution than the quantized data by performingbinarization processing to each of the plurality of quantized datacorresponding to the plurality of relative movements, and, when thesecond mode has been set by the setting unit, (D) generate a binary datafor the same color by performing binarization processing of the inputimage data, and (E) divide the binary data for the same color todivisions corresponding to the plurality of relative movements.
 7. Animage processor for processing input image data that corresponds to apixel area in order to perform printing in the pixel area on a printingmedium by a plurality of relative movements of a printing unit forprinting a same color dot, with respect to the printing medium,comprising: a setting unit configured to set one mode from among aplurality of printing modes that include a first mode for printing inthe pixel area by performing M (where M is an integer larger than 2)number of relative movements, and a second mode for printing in thepixel area by performing N (where N is an integer larger than 3 and N>M)number of relative movements; and a processing unit configured to, whenthe first mode has been set by the setting unit, (A) generate aplurality of multi-value image data for the same color corresponding tothe plurality of relative movements, that have a lower resolution thanthe input image data, based on the input image data, (B) generate aplurality of quantized data corresponding to the plurality of relativemovements, by performing quantization processing to each of theplurality of multi-value image data for the same color corresponding tothe plurality of relative movements, and (C) generate a plurality ofbinary data corresponding to the plurality of relative movements, thathave a higher resolution than the quantized data by performingbinarization processing to each of the plurality of quantized datacorresponding to the plurality of relative movements, and, when thesecond mode has been set by the setting unit, (D) generate a pluralityof multi-value data corresponding to the plurality of relativemovements, that have a resolution equal to the resolution of the inputimage data, based on the input image data, and (E) generate a pluralityof binary data corresponding to the plurality of relative movements, byperforming binarization processing to each of the plurality ofmulti-value image data for the same color corresponding to the pluralityof relative movements.
 8. An image processing method for processinginput image data that corresponds to a pixel area in order to performprinting in the pixel area on a printing medium by a plurality ofrelative movements of a printing unit for printing a same color dot,with respect to the printing medium, comprising: a step of generating aplurality of multi-value image data for the same color corresponding tothe plurality of relative movements, that have a lower resolution thanthe input image data, based on the input image data; a step ofgenerating a plurality of quantized data corresponding to the pluralityof relative movements by performing quantization processing to each ofthe plurality of multi-value image data for the same color correspondingto the plurality of relative movements; and a step of generating aplurality of binary data for the same color corresponding to theplurality of relative movements, that have a higher resolution than thequantized data, by performing binarization processing to each of theplurality of quantized data corresponding to the plurality of relativemovements.